Problem using the database vocabulary in Business Rule

    My input message schema to BizTalk orchestration has a tag for OfficeID. I need to check whether the OfficeID is a valid one by checking it with the master list of Office IDs from a database table. I want to do this using BRE and accordingly set the IsAllowed flag in the message.

   To implement the Business Rule, I have created a database vocabulary which maps to the database table column for master list of Office IDs. But I am not getting any predicate to construct the condition of the rule, which will check whether the Office ID in message actually exists in database vocabulary. Can you please help me with your guidance?

Thanks,

Ankur.